Snap action device



April 21, 1959 J. w. CROWNOVER 2,382,678

SNAP ACTION DEVICE Filed NOV. 15, 1954 /e -/3 /a l6 /0 AWIWQ F/Gl. 3

INVENTOR JOSEPH W. GROWNOl/ER ATTORNEY United States Patent SNAP ACTIONDEVICE Joseph W. Crownover, Sherman Oaks, Calif., assignor to ElectricMachinery Mfg. Company, a corporation of Minnesota Application November15, 1954, Serial No. 468,975

11 Claims. (Cl. 60-23) This invention relates to a snap action device,and particularly to an improved snap action movement utilizing a snapspring which is particularly adaptable for utilization in connectionwith an electrostrictive or piezoelectric actuator, that is, in anelectrical relay, wherein contacts are actuatable by such an actuator.The invention is, however, not limited to this application; it may beutilized in any application wherein snap action is desired. It isparticularly advantageous and adaptable in the aforesaid applicationhowever, because of the relatively low operating energies developed bythe electrostrictive or piezoelectric actuators. These actuators usuallytake the form of ceramic bi-element units, and the small energiesdeveloped necessitate that the snap action mechanism be very sensitive.In the past it has been found that in order to realize this greatsensitivity it has been found necessary to use low stress snap springs.In the prior art the snap springs utilized have been quite commonlysupported on knife edge mountings, and due to the low stress in thesprings they were subject to the defect and deficiency that the springswere easily jarred loose, sliding along the knife-edged supports andthus getting out of adjustment and causing the device to fail. Mostmodern applications of electrical relays and similar components requirethat they be built to very rigid specifications; particularly thecomponents must be able to stand jarring, vibration, shocks, severeacceleration forces, and many other relatively harsh conditions. Suchconditions occur in such applications as guided missiles, high-speedmachinery subject to vibration, devices operated at ex-, tremely highvelocities, etc.

The prior art has also been subject to the deficiency ofdeterioration ofthe snap springs utilized, and particularly that ordinarily the snapmember has a crimped or deformed portion which, being subject torepeated flexures is subject to unpredictable failure; that is, stressesare set up at a certain point in a part or member of the snap device byway of a deformation, there being fiexure at the. deformation each timethat the device is snapped. The deformed portion is a weakened area, andafter repeated flexures this portion is very apt to fail, and sinceordinarily the snap device is subjected to many thousands of flexures,it can be seen that the rate of failures is apt to be high. The presentinvention provides a snap spring wherein this deficiency is overcome inthat the deformed area which sets up the stresses is relatively smalland is completely engaged, that is, clamped, by a supporting member suchthat there is no flexure of the deformed area at all. The snap springbeing mounted by a clamp in this manner, precluding flexure of thedeformed area, is also characterized in that it has extremely stableoperating characteristics. Thus, the invention provides a snap actiondevice which, although it is extremely sensitive, overcomes the majordeficiencies of the prior art, and this has been accomplished by way ofan extremely simple device as will appear in the detailed specificationhereinafter. Generally the device takes the form of a strip of'metalhaving a longitudinal slot forming two spaced reaches. The deformationis provided at an intermediate point of one of these reaches near oneedge thereof, and the deformation is characterized in that itconstitutes a mashing or flattening of the metal without deformation outof the plane of the strip, with the result that stresses are set up inadjacent portions of the strip which are torsional in nature so as to betransmitted to the other reach as a bending moment. The detailedtechnical characteristics of the device will appear in the specificationhereinafter.

It is accordingly an object of the invention to provide an extremelysensitive snap action device having a rigid mounting, but which isoperable in response to the low energies developed by such devices aselectrostrictive capacitive actuators.

Another object of the invention is to provide a snap action devicehaving spaced parallel reaches, one of which has an intermediatedeformation setting up stresses whereby the strip is operable to snapbetween oppositely bowed positions, the device being rigidly mounted atsaid deformed portion to preclude flexing at said portion.

Another object of the invention is to provide a snap action devicecomprising a strip of metal having a longitudinal slot forming parallelreaches, one of the reaches having an intermediate mashed portionadjacent one edge thereof, the strip being mounted and clamped at saidportion, and being operable to snap between oppositely bowed positions.

In one form of the invention the device is constructed as a unitarybi-element device wherein an external force is not applied for producingthe snap action, but rather, the device snaps by warping in the mannerof a bi-element thermostat. In this form of the invention anelectrostrictive ceramic element is bonded to one reach of the snapspring, and upon the application of voltage to the electrostrictiveelement it deforms in a manner such that by reason of its being bondedto the snap spring it causes warping thereof and resultant snapping.

It is, accordingly, an object of my invention to provide a snap actiondevice having characteristics as in the foregoing, wherein the deviceincludes an electrostrictive ceramic element bonded to a part thereof insuch manner as to cause snapping of the device in response to theapplication of voltage to the ceramic element.

Further objects and numerous of the advantages of the invention willbecome apparent from the following detailed description and annexeddrawings, wherein:

Fig. 1 is a plan view of a preferred form of snap action device of myinvention;

Fig. 2 is a side elevation of the device of Fig. 1;

Fig. 3 is a detail sectional view taken along line 3-3 of Fig. 1;

Fig. 4 is a perspective view of the snap action device of the previousfigures;

Fig. 5 is a perspective view of the snap action device showing themanner in which it is mounted;

Fig. 6 is a view of a modified form of my invention;

Fig. 7 is a view of a modified form of mounting of the snap spring; and

Fig. 8 is a view of a form of the invention wherein the spring is formedof bi-element, or bi-metal material.

Referring to Fig. 1 of the drawings, the snap action device is shown inthe form of a metal strip as indicated at 10, which may be formed of anyof the metals or alloys used in the prior art as snap springs. The striphas a longitudinal slot as shown at 11, having arcuate ends. Thelongitudinal slot provides two parallel reaches as indicated at 13 and14, the reach 14 being somewhat longer as shown, to form a contactcarrying portion and an actuator, as will be described.

The two reaches are joined by rounded transverse 'portions of the stripas indicated at 15- and 16.

assaere The strip is characterized by having certain permanent stressesprovided therein such that the strip can snap between oppositely bowedpositions of stable equilibrium. The particular way in which thepermanent stresses are set up: and the effect of these stresses upon thevarious portions of the device, are an important feature of theinvention. The reach 13 has an intermediate deformed portion as shown at17, which is a mashed or flattened portion, that is, this portion ismashed such as by pounding or hammering it against an anvil or the like,without actually deforming the portion out of the plane of the reach 13.The deformed portion 17 is largely adjacent one edge of the reach 13;that is, more of the deformed area is adjacent the inner edge of thereach 13. The effect of this mashing or. compacting of the metal is toset up certain stresses in the portions of the reach 13 adjacent themashed area 17. The effect of the mashing is to cause a flow of themetal which tends to make the inner edges of the portions of reach 13adjacent the area 17 elongate. This tendency manifests itself actuallyas a torsional stress in the portions of reach 13 adjacent the area 17.This torsional stress in the metal is represented by the curved arrows18, and it transmits itself through the transverse portions 15 and 16 asa bending moment to the longer reach 14. In order to more explicitlyexplain this torsional stress and its effect as a bending moment inreach 14, the broken line 21 represents a crank whereby a torque ortwist can be exerted about the axis through the center of reach 13represented by line 22. In other words, the torsion represented by thecurved arrow 18 is trans mitted as a bending moment to the reach 14which is in effect equivalent to a downward force being exerted at thepoint 23. The effect becomes more clearly understandable when the effectof a counterrotationas ap plied to the crank 21, is observed. Forexample, if an upward force, as indicated at 24, is applied to the endof the reach 14, it will be observed that the crank as diagrammaticallyillustrated at 21, tends to apply torque or rotation about the axis 22opposite to the arrow 18. In other words, the efiect of the upward force24 through the crank 21 is to apply a countertorsional stress to theportion of reach 13 adjacent the area 17. The original effect of thetorsional stress as described is to cause the strip to bow into aconformation as shown in Fig. 2. When a reverse force, as indicated at24, is applied set ting up the countertorsional stresses, the efiect isthat the strip will snap to a reverse position of stable equilibrium.

The reach 14 of the strip has contact members 27 and 28 at its left end,which may operate between fixed contacts not shown. The mounting of thestrip is an extremely significant feature of the invention for reasonswhich will be pointed out. The strip is mounted by way of a rigidmounting or clamping bracket 30 having a slot 31 as shown, which engagesthe reach 13 of the device, and rigidly engages over and clamps the areaof reach 13 embracing the mashed or deformed portion 17. Thus, when thestrip snaps from a bowed position as shown in Fig. 2, to an upwardlybowed position, while there is bending action of the metal, it can beseen that there is no flexing of the mashed area 17 since it is whollywithin the clamping area of the bracket 30. Thus, even if the deformingof this area structurally weakens it, this is of no concern since thearea, if it is weakened, is wholly within the rigid clamping bracket andis supported thereby. From Fig. 5 the operation described above can bereadily understood. as related to the mounting bracket 30. As described,the force as exerted at 24 to one end of the reach 1.4 appliescountertorsional stresses such that the strip as a whole snaps to areversely bowed position wherein the torsional stresses in the portionsof reach 13 adjacent the area 17 are in a direction opposite to that.indicated by 4; r the arrow 18 and with a resultant reverse bendingmoment applied to the reach 14.

As will be observed from the foregoing, the structure is one wherein thesnap strip or device is mounted at an intermediate point with portionsextending in each direction therefrom. This is to be distinguished fromthe prior art type of cantilever device wherein a snap acting member isrigidly mounted at one end. The nature of a cantilever type of mountingis such that a greater amount of space. is" required to provide a devicehaving comparable capacity to interrupt an electrical circuit or thelike, since a considerable part of the beam is utilized by its mounting;

It will be observed that in each of the oppositely bowed positions ofthe strip it is in a condition of stress equilibrium, that is, a stablecondition. The device readily adapts itself to varying or controllingthe forcedisplacement ratio; that is, the ratio as between the operatingforce required and the displacement or movement imparted to theelectrical contacts 27 and 28. The bending moment transmitted to thereach 14 by the torsional stresses in the reach 13 depends on therelative lengths of the portions of reach 13 on each side of the area17, and thus the bending moment and consequently the operating forcerequired can be varied by varying the lengths of these portions relativeto the overhang of the reach 14. In other words, if the overhang isincreased, the operating force ratio is reduced and the displacement isincreased.

The invention lends itself readily to production and fabricationinasmuch as the strips can be simply stamped out of suitable metal. Thedeformation 17 is easily provided in the reach 13, and the resultantsnap action device is extremely rugged, stable, and possesses highlysatisfactory snap action characteristics. The device can be manufacturedvery satisfactorily in miniature sizes, and as pointed out in theforegoing, is particularly useful with electrostrictive capacitiveactuators in view of the low operating energies required. Even inminiature sizes however, the device is capable of interrupting currentsof considerable magnitude.

Referring to Fig. 6 of the drawings, there is shown a modified form ofmy invention wherein it is unnecessary to provide an external operatingforce for causing snapping operation of the spring. In the form of theinvention shown in Fig. 6, the snap spring 10 is similar to that of theprevious embodiment. It has a similar intermediate deformed portion asin the previous embodiment, and it is similarly mounted in a mount 30.In Fig. 6, however, there is bonded to the reach 14 an electrostrictiveceramic element designated by the numeral 34. The element 34 may be ofvarious materials having electrostrictive properties, but may preferablybe formed of a barium titanate ceramic of the type shown in my previousPatent No. 2,800,551. The material of the element 34 has thecharacteristic that when 2. volt.- age is applied across the thicknessof the element it expands in thickness and contracts in lengthirrespective of the polarity of the applied voltage in the mannerdescribed in the previous applications. The member 34 has an electrode35 formed on its outer face, which may be simply by painting its outersurface with an electrically conductive paint, as silver paint. Thereach 14 of the spring 10 forms an electrode bonded to the opposite faceof the member 34. Numeral 37 designates a contact bracket from whichelectrical connections are made as shown, to the electrode 35. A secondcontact 38 is attached to the mount 30 as shown, so that vthe reach 14of the snap spring 10. forms the second electrode of theelectrostrictive unit. By applying an appropriate potential between thecontact members 37 and 38, this potential may be applied across thethickness of the element 34. When a potential is so applied, the element34 expands in thickness and contracts longitudinally. It thus operatesto cause warping of itself and the reach 14 in the manner of a bimetalthermostat. The operation is then substantially the same as in theprevious embodiment. The warping of the reach 14 reflects a torsional ortwisting moment back into the parts of the reach 13 adjacent the mount30, and when the warping is sufficient, the spring will snap betweenoppositely bowed positions as in the previous embodiment. Thus, the snapdevice requires no separate actuating or operating mechanism capable ofdeveloping an operating force. The device is thus completely unitary,integrated and fully operative within itself, simply by the applicationof an appropriate voltage thereto.

Numeral 40 designates a contact bar or member having electricalcontactors 41 and 42 at its ends. The contact 41 moves between fixedelectrical contacts 43 and 44, and the contact 42 moves between fixedelectrical contacts 46 and 47. The contact bar 40 is attached to andspaced from the snap spring 10 by stand-off insulators 49 and 50. In thepresent embodiment of the invention as will be observed, both ends ofthe snap spring 10 are available for the actuation of contacts of acontactor member. Thus, the device readily adapts itself for theactuation of multiple contacts as shown in Fig. 6. It is apparent thatthe device adapts itself to extremely compact construction even thoughmultiple circuit controlling functions are present.

In the device of Fig. 6 the elements 34 and 14 may have the same ordifferent coefficients of thermal expansion. If they are the same theeffect is to compensate for temperature changes and the device isresponsive only to voltage. Otherwise, the device responds at atemperature dependent on the applied voltage.

Referring to Fig. 7 of the drawings, there is shown another form of theinvention which adapts itself favorably to production techniques. Themodification of Fig. 7 embodies a snapcspring 10, as in the previousembodiments. The embodiment of Fig. 7 utilizes a mounting bracket 52which is slightly different than that of the previous embodimentspermitting easy and simplified fabrication and assembly, and havingcertain other advantages. The bracket 52 is mounted by rivets as shownat 53, and has a resilient extending portion 54. The reach 13 of thesnap spring has an extending tab 55 at the mashed or flattened area,which, in the present embodiment, is adjacent the outer edge of thereach 13. The snap spring is attached to the portion 54 by a bolt 56extending through the aperture in the tab 55 and through a washer 59,the washer completely covering the mashed area. Thus, the washerprovides a rigid member over the mashed area such that as in theprevious embodiment, there can be no flexing of the mashed area. In thepresent embodiment the necessity of milling a slot in the mountingbracket is eliminated, and the use of solder in attaching the snapspring is avoided. Thus, the possibility of any solder running down ontothe reach 13 and changing its characteristics, is avoided. At the end ofthe portion 54 is an adjusting screw 60 which bears against a rigidsurface so that the portion 54 can be adjusted toward and away from thesurface to thereby adjust the mounting position of the snap spring 10,and accordingly, the position of the contact 41 relative to the fixedcontact with which it cooperates. In the present embodiment theoperating force is applied to the left end of the reach 14 as in thefirst embodiment.

Fig. 8 shows a form of the invention wherein the spring is formed ofconventional bi-element or bi-metal material so that a temperatureresponsive snap acting device is formed. The characteristics of thedevice are otherwise the same as previous embodiments.

The foregoing is a representative disclosure of preferred forms of myinvention. It is intended that the disclosure be interpreted as beingillustrative rather than limiting upon the invention, and it is alsointended that all variations and modifications which may be made by"those skilled in the art come within the scope and meaning of theclaims appended hereto.

I claim:

1. A snap action device, comprising: a strip of spring material having alongitudinal slot whereby two parallel reaches are formed, one of saidreaches having a deformation at an intermediate portion thereof, rigidmounting means engaging said strip at said deformation whereby flexingof the material at said deformation is precluded, the deformation beingof such character as to produce stresses in the device, causing it tobow out of a plane whereby upon the application of a reversely bowingforce to one end of the device it bows in the reverse direction with asnap action.

2. A snap action device, comprising: a strip of spring material having aplurality of portions, the material having a deformation intermediateits ends; mounting means engaging the strip and clamping the deformedarea so. as to preclude any flexing of the deformed material, thedeformation being of a character to produce deforming stresses inportions of the material adjacent the mounting means, whereby the stripdeforms out of a plane, the deformed strip having the characteristicthat upon applying a counterdeforming force to one end of the strip itdeforms in the opposite direction with a snap action.

3. A snap action device, comprising:' a strip of spring material havinga plurality of portions, the material having a permanent deformationintermediate its ends, the deformation comprising a relatively smallarea wherein the material is mashed to a lesser thickness than adjacentportions such that deforming stresses are set up in the adjacentportions, said area being located adjacent an edge of said strip; meansrigidly supporting said strip at said area, said stresses producing abending deformation in said strip, the strip having the characteristicthat upon the application of a reverse bending moment the strip deformsin the opposite direction with a snap action.

4. The structure of claim 3, wherein said supporting means engages thearea of said deformation so as to preclude any flexing of the deformedarea.

5. A snapaction device, comprising: a strip of spring material having aplurality of portions, the material having a permanent deformationintermediate its ends, the deformation comprising a relatively smallarea wherein the material is mashed to a lesser thickness than adjacentportions such that deforming stresses are set up in the adjacentportions; and means rigidly supporting said strip at said area,including a washer clamped over the deformation to preclude flexing ofthe material at said deformation, said stresses producing a bendingmoment in said strip, and the strip having the characteristic that uponthe application of a reverse bending moment the strip deforms in theopposite direction with a snap action.

6. A snap action device, comprising: a strip of spring material having alongitudinal slot whereby two parallel reaches are formed, at least oneof said reaches having a permanent deformation intermediate its ends,the deformation comprising a relatively small area wherein the materialis mashed to a lesser thickness than adjacent portions; means formounting said strip at the area of said deformation, the deformationcausing torsional stresses to be set up in the adjacent portions of thesaid one reach which are transmitted as a bending moment to the otherreach, causing bowing of the strip, the strip having the characteristicthat upon the application of a reverse bending moment, counter-torsionalstresses are set up in the portions adjacent the mounting means wherebythe strip bows in the opposite direction with a snap action, themounting means engaging the strip in such manner as to preclude anyflexing of the permanently deformed area.

7. A snap spring, comprising: a strip of metal having an intermediatepermanently deformed area, the defor- 7 mation comprising a relativelysmall area in which the metal is mashed to have a lesserthickness thanother portions of the strip, without the deformed area being otherwiseout of the plane of the strip, the deformation Setting up stresses inthe strip such that if the, strip is fixed it will flex with a snapaction between first and second positions and supporting means for thesaid strip, the supporting means engaging the deformed area so as topreclude any flexing of material at said deformed area.

8.. A. snap spring, comprising a strip of metal having a longitudinalslot forming parallel reaches, one of said reaches having anintermediate permanently deformed area, the deformation comprising arelatively small area adjacent one edge of the said one reach in whichthe metal is mashed to have a lesser thickness than other portions ofthe strip without the: deformed area being otherwise out of the plane.of the strip, the deformation setting up torsional stresses in thematerial adjacent to the deformation, which are transmitted to the otherreach as a bending moment causing bowing of the strip out of a plane,the strip having the characteristic that upon the application of areverse bending moment thereto counter-torsional stresses are set up,causing the strip to move to a reversely bowed position with a snapaction; and mounting means for the said strip, the mounting meansengaging the permanently deformed area so as to preclude any flexing ofthe deformed area.

9. A snap action device, comprising: a strip of spring material having alongitudinal slot to form first and second laterally spaced reaches, oneof said reaches being fixedly mounted. at an intermediate point betweenthe ends of the said slot and its ends being. free, one of said reaches.having adeformed portion adjacent and intermediate the ends of the slotsuch that adjacent portions of said one. reach tend to deform out. of aplane by twisting, setting up torsional stresses. therein, which aretransmitted through said one reach to said other reach as a bendingmoment causing bowing of the other reach, whereby upon applying areverse bowing moment to said other reach a counter torsion is appliedto said portions, causing them to deform in the opposite direction witha snap action and similarly reversing the bowing in said other reach.

10. A snap action device, comprising: a strip of spring material havingalongitudinal slot whereby two parallel reaches are formed, one of saidreaches having a permanentdeformation intermediate its end andintermediate the length of the slot, the. deformation comprising arelatively smallarea wherein the material is mashed to a lesserthickness than adjacent portions; mounting means fixedly engaging saidone reach at the area of said deformation, and the ends of the stripbeing free, the deformation causing torsional stresses to be set up inthe adjacent portions of the said one reach which are transmittedthrough said reach as a bending moment to the other reach, causingbowing of the said other reach, the strip having the characteristic thatupon the application of a reverse bending moment counter torsionalstresses are set up in the portions adjacent the mounting means wherebythe strip bows in the opposite direction with a snap action.

lL-A snap spring comprising: a strip of metal having a longitudinal slotforming parallel. reaches, one of said reaches having an intermediatepermanently deformed area, the deformation comprising a relatively smallarea adjacent one edge of the said one reach in which the metal ismashed to have a lesser thickness than other portions of the strip.without the deformed area being otherwise out of the plane of the strip,the deformation setting up torsional stresses in the material adjacentthe deformation, which are transmitted to the other reach as a bendingmoment causing bowing of the strip out of a plane, the strip having thecharacteristic that upon the application of a reverse bending momentthereto counter-torsional stresses are set up causing the strip to moveto a reversely bowed position with a snap action, and mounting meanscomprising a bracket, the snap spring having anv aperture thereinadjacent the deformed area and means comprising a bolt extending throughthe aperture and the bracket and. having a washer completely coveringthe deformed area to provide a rigid backing therefor.

References Cited in the file of this patent UNITED STATES PATENTS1,952,895 Ross Mar. 27, 1934 2,361,202 Hodgkins Oct. 24, 1944 2,363,280Arnold Nov. 21, 1944 2,511,526 Bugge- June 13, 1950 2,640,889 CherryJune 2, 1953 2,692,317 Bletz Oct. 19, 1954

